In the art of making aluminum complex greases, two methods of preparation are commonly employed. In one of these methods, an aluminum alkoxide is dissolved in oil stock and two mole equivalents of an acid or acid mixture is added thereto. During subsequent heating, reaction occurred releasing one mole of alcohol per mole of acid introduced. Thereafter, to the resulting system water is added which reacts with the final remaining alkoxy group, thereby releasing the third and final mole of alcohol and producing a hydroxyl group on the aluminum atom. The alcohol produced is removed by distillation, and, since the water is typically added in excess, the excess water is likewise removed by distillation. A typical aluminum alkoxide employed in this method is aluminum isopropoxide; see, for example U.S. Pat. No. 3,345,291 issued to Chevron Research Corporation.
In the second technique, a cyclic aluminum isopropoxide (or other alkoxide) trimer is introduced into a mineral oil. To this mixture is added a carboxylic acid mixture which is appoximately equal to two moles of acid per mole of aluminum. When this mixture is heated, reaction occurs which releases one mole of alcohol per mole of aluminum; see, for example, Rinse U.S. Pat. No. 3,054,816. Apparently, it is possible to reverse the order of addition so that the cyclic aluminum isopropoxide trimer is added after the acids are introduced into the petroleum oil; see, for example, column 4 of Bailey et al U.S. Pat. No. 3,776,846. The alcohol thus produced as a by-product is removed by distillation.
Recently, one of us discovered a class of oxyaluminum acylates which can be used in combination with organic acids to prepare commercially greases of mineral oils in such a way as to avoid the problems of removing alcohol produced as a by-product in the grease manufacture and to avoid the addition and/or removal of water present in a system; see Pratt U.S. Ser. No. 096,933. In Rinse U.S. Pat. No. 3,054,816 (see column 3, lines 53-57), it is suggested that a cyclic aluminum oxide stearate trimer can be mixed with mineral oil and then reacted with benzoic acid at elevated temperature to produce a grease. This suggestion of Rinse, so far as is known, has never been commercially exploited. Moreover, the properties of the grease made by the Rinse procedure are not equivalent to the properties of greases made by using oxyaluminum acylates wherein the ratio of the number of aromatic radicals to aliphatic radicals of the cyclic trimer compound range higher than about 3:1.
In Harson British Pat. No. 825,878 cyclic organoaluminum trimers and linear organoaluminum polymers are used in greases. Thus, mixed benzoate/stearate oxylauminum acylate trimers are shown (see page 4, lines 100-110, Example 3, and Example 17 of Harson), as greases made with cyclic trimers (see Examples 25 and 28). Harson used only low amounts of benzoic acids in his organoaluminum compounds (not more than 35 mole percent) and he experienced difficulty in making smooth greases without lumping. In Example 28 thereof for example, when benzoic acid is present in the "external acids", certain other acids (such as branched chain and short chain acids or dimer acids or unsaturated acids or hydrogenated castor fatty acids must be present. Also, presolution of benzoic acid is needed therein to get a smooth grease. Harson never utilized oxyaluminum acylates wherein the ratio of number of aromatic radicals to aliphatic radicals of the cyclic trimer compounds was higher than about 3:1.
The previous above-referenced oxyaluminum acylates of Pratt (see U.S. Ser. No. 096,933) which contain up to 75 mole percent of aromatic carboxylic acid were mainly prepared by utilizing three carboxylic acids: An aromatic acid, an aliphatic acid, and a lower alkanoic acid. The lower alkanoic acid, during the synthetic preparation procedure, produces, as explained in U.S. Ser. No. 096,933, an ester by-product which is easily volatilized and removed. However, oxyaluminum acylates containing more than about 75 mole percent of aromatic carboxylic acid were found to be generally inoperative for use in the manufacture of aluminum complex greases when made by the three acid route.
Now it has been discovered that new oxyaluminum acylates containing more than about 75 mole percent of an aromatic carboxylic acid, but less than about 95 mole percent of aromatic acid, can be prepared, and, further, that such new oxyaluminum acylates can be used to make aluminum complex greases of seemingly excellent quality. The general compound preparation method employed to make such new oxyaluminum acylates was previously discovered by one of us and is readily applicable for the making of such compounds. The greases made from such new oxyaluminum acylates are produced without the use of water and without the production of water or alcohol as by-products.
The compound preparation method employed to make such new oxyaluminum acylates utilizes only two carboxylic acids for reaction with a starting aluminum alkoxide, and the product new oxyaluminum acylates so made are characteristically clear, homgeneous, relatively low melting materials which are substantially soluble in the organic liquids used to make greases. In contrast, when these same new oxyaluminum acylates are synthesized by the three acid route, the product acylates are not clear, but are heterogeneous in composition, and are not substantially soluble in such organic liquids. Furthermore, greases made with such product acylates are not uniform and characteristically contain opaque solid particles. It is now theorized (but there is no intent to be bound herein by theory) that the three acid route results in the production of product oxyaluminum acylates which contain lower alkanoate substituents which cause such undesirable properties for grease making purposes when one is dealing with oxyaluminum acylates containing more that about 75 mole percent of aromatic carboxylic acid.
By such evidence and reasoning, it is concluded that an oxyaluminum acylate containing more than 75 mole percent aromatic carboxylic acid which is to be used in complex aluminum grease manufacture should preferably not contain any substantial quantity of oxyaluminum acylate wherein the acylate substituents are derived from a lower alkanoic acid (such as acetic acid), in order to make a product grease of uniform, homgeneous texture. Such lower alkanoic acid containing oxyaluminum acylates are high melting products which are theorized to be difficultly dispersable in the liquids normally used to make greases which in turn makes good greases very difficult if not impossible to prepare therefrom.
An all-aromatic oxyaluminum acylate is known to the prior art. Thus, Rinse in U.S. Pat. No. 2,913,468 discloses, in Example 4 thereof, preparation of a compound which can be considered to be identified as oxyaluminum benzoate, allegedly made by the method sometimes termed by those skilled in the art as the controlled hydrolysis method.
In the laboratory, an endeavor was undertaken to make by these teachings of Rinse in such '468 patent oxyaluminum benzoate, and it was also undertaken to prepare oxyaluminum benzoate by the route herein used to make the novel mixed aromatic/aliphatic oxyaluminum acylates of the present invention. By each such route, there was prepared a product which was heterogeneous, not clear to transmitted light, and relatively high melting. Also, each product, so far as is now known, is not appreciably soluble in liquid hydrocarbons of the type conventionally used to make greases.
Laboratory work in connection with the utilization of oxyaluminum acylates in aluminum complex greases seems clearly to indicate that higher quality greases are made when a substantially homogeneous oxyaluminum acylate is employed, an homogeneous oxyaluminum acylate being preparable routinely from mixed aromatic and aliphatic carboxylic acids as provided in the present invention. The presence of even a relatively very small amount of an aliphatic carboxylic acid containing Type (A) radicals (as hereinbelow identified) appears to very substantially enhance the homogeneity and the low melting character of a product oxyaluminum acylate as well as the solubility thereof in liquid hydrocarbons of the type conventionally used to make greases. When, however, an oxyaluminum acylate is heterogeneous, it appears that a product grease which is clear in texture is difficult to obtain.
A further consideration in this invention is the circumstance that it appears, for reasons not now understood, that an aluminum alkoxide does not react to molar completion with a single species of aromatic acid, such as benzoic acid, so that inherently such a reaction system tends to produce a non-uniform reaction product which itself is not, it is theorized, desirable for use in making aluminum complex greases.
Therefore, all-aromatic oxyaluminum acylates are not believed to be suitable for use in the manufacture of aluminum complex greases.